1. Field of the Invention
The present invention generally relates to automotive instrument clusters. More specifically, the invention relates to instrument clusters where a display is located in front of an analog gage while allowing the analog pointer to remain visible.
2. Description of Related Art
Originally, automobile instruments were analog devices. Using mechanical or electro-mechanical means, they displayed the operational status and performance of a motor vehicle. However, only factors that could be directly measured could be displayed to the driver. Common gages of this type are speedometers, tachometers, odometers, fuel level, oil pressure and the like. Each of these analog gages are connected to a sensor providing a signal in direct proportion to the value being measured.
As technology has advanced, analog gages and sensors have been replaced by digital sensors and gages. A digital instrument panel, rather than being connected directly to the sensors monitoring the performance of the vehicle, is connected to a digital controller that is connected to the sensors. The controller then monitors the output of the sensors, processes the information, and displays the information on the instrument panel to display in a manner useful to the driver.
Various types of digital indicators may be used. Numeric digital displays have been used where, for example, the speed of the vehicle was displayed in an alpha-numeric lighted display. Other indicators included LCD's for the display of secondary information, such as mileage or oil pressure.
Some information is more readily interpreted using a digital display. For example, rather than lighting a generic “check engine” light when a problem is detected by the controller, a digital display allows the controller to display more detailed information, such as “change oil” or “low tire pressure.” In addition, a single digital display can have multiple functions, thereby saving space. Finally, if a large color display used, it is possible for the controller to include a navigation system. Such a configuration may display navigational maps which, when incorporated with a global positioning system (GPS), can display the vehicle's location.
Despite the flexibility of digital indicators and displays, consumers have consistently preferred the behavior and appearance of traditional analog gages. These may be used in conjunction with a digital controller by attaching a pointer indicator to a small electric motor electrically coupled to the controller. The controller then commands the motor to move the pointer between numbers on a scale representing, for example, miles per hour, printed on the instrument panel.
One drawback of large digital displays is that they occupy a significant amount of area. Therefore, if an LCD, for example, is included, some analog indicators may be omitted. As mentioned earlier, many consumers of motor vehicles prefer analog indicators to monitor certain parameters. Some of these indicators, such as speed, may be quite large. This limits the amount of space available for a large digital display, such as an LCD.
However, the center of a typical analog indicator has no significant function. The movement of the end of the pointer is what conveys the desired information to the driver. Thus, the center of an analog indicator provides space that may be used for other purposes. As a result, many instrument clusters use this location to install large LCD's, or other digital displays, while retaining the analog indicators and minimizing the space occupied on the instrument cluster.
However, in order to avoid having the LCD interfere with the analog gage, it is usually cantilevered in front of the pointer. This allows the pointer to move freely through its range of motion, but still allows the display to be positioned in the center of the gage.
A drawback to this configuration is that existing displays are cantilevered in front of the analog indicator using a simple, plastic frame. While plastic has the advantage of being a light weight, inexpensive material, it has a number of disadvantages. For example, plastic is a high dielectric material, has low stiffness, and has poor thermal conductivity.
Thus, plastic frames are an efficient supporter of electrostatic fields, which exacerbates the Tribo Electric Effect. The Tribo Electric Effect is where a static charge is allowed to build on the LCD and discolor the output of the display. In addition, such displays are relatively heavy, and the low stiffness of the plastic frame allows it deflect and vibrate as the vehicle moves. As a result, the display may interfere with the analog gage and this necessitates the provision of a large gap between the display and the gage to allow for deflection. As a result, the overall thickness of the instrument cluster is increased. Because of poor thermal conductivity, heat can build up and may limit the brightness of the display. This in turn may limit the current at which the display may be driven.
In view of the above, it is apparent that there exists a need for an improved display frame that overcomes the disadvantages and limitations of the known technology.